1. Field of the Invention
The present invention relates to a corrosive-resistant soft magnetic film formed of a CoFe alloy, which is used, for example, for the core of thin-film magnetic heads, having a saturation magnetic flux density larger than that of NiFe alloys. The present invention also relates to a thin-film magnetic head using the soft magnetic film and further relates to methods of manufacturing the soft magnetic film and the thin-film magnetic head.
2. Description of the Related Art
As the demand for a high recording density has been increasing, a magnetic material having a high saturation magnetic flux density Bs has been required to be used for, for example, the core layer of a thin-film magnetic head so that the magnetic flux is concentrated in the vicinity of the gap in the core to improve the recording density.
NiFe alloys are typically used for a magnetic material. The NiFe alloys are formed by electroplating with direct current and have a saturation magnetic flux density Bs of about 1.8 T.
In order to increase the saturation magnetic flux density of the NiFe alloys, for example, a pulsed current has been used for electroplating instead of using a direct current.
Thus, the saturation magnetic flux density Bs of the NiFe alloys has been improved. However, the Bs is at most 1.9 T and a Bs of 2.0 T or more is rarely achieved.
Increasing the saturation magnetic flux density Bs causes the film surface to become rough, and consequently the NiFe alloys are readily eroded by various solvents used for manufacturing the thin-film magnetic heads.
Alternatively, CoFe alloys are often used for a magnetic material. The Co content of a typical CoFe alloy is about 50 mass %, and such a composition ratio results in a film having a low saturation magnetic flux density Bs and an extremely rough surface, and therefore the film can be eroded.
Accordingly, an object of the present invention is to provide a corrosion-resistant soft magnetic CoFe alloy film having a saturation magnetic flux density Bs higher than that of NiFe alloys, a thin-film magnetic head using the soft magnetic film, and methods of manufacturing the soft magnetic film and the magnetic head.
To this end, according to one aspect of the present invention, there is provided a soft magnetic film comprising a composition expressed by the formula Co1-xFex. The Fe content X is in the range of 68 to 80 mass %.
The soft magnetic film may have a saturation magnetic flux density Bs of 2.0 T or more, and preferably the saturation magnetic flux density Bs is 2.25 T or more.
Thus, the film is prevented from having a large crystalline grain size and can have a dense crystal; hence the corrosive resistant soft magnetic film can be manufactured.
The soft magnetic film may have a center line average roughness of the surface of 9 nm or less.
By preventing the film from having a large crystalline grain size, a low coercive force Hc can be achieved.
Preferably, the soft magnetic film is formed by plating, thereby having a desired thicker film thickness than those of films formed by sputtering.
According to another aspect of the present invention, a thin-film magnetic head is provided. The thin-film magnetic head comprises a lower core layer formed with a magnetic material, a magnetic gap, and an upper core layer. The upper core layer opposes the lower core layer with the magnetic gap there between at the face opposing a recording medium of the magnetic head. A coil layer is also comprised to apply a recording magnetic field to the lower and the upper core layers. The lower core layer or the upper core layer is formed of the soft magnetic film.
Preferably, the thin-film magnetic head may further comprise a lower magnetic pole layer formed of the soft magnetic film on the lower core layer and at the face opposing a recording medium thereof.
According to another aspect of the present invention, there is provided a thin-film magnetic head comprising a lower core layer, an upper core layer, and a magnetic pole lying between the lower core layer and the upper core layer. The magnetic pole has a shorter width in the track width direction than those of the lower and the upper core layers. The magnetic pole comprises a lower magnetic pole layer in contact with the lower core layer, an upper magnetic pole layer in contact with the upper core layer, and a gap layer lying between the lower magnetic pole layer and the upper magnetic pole layer. Alternatively, the magnetic pole comprises an upper magnetic pole layer in contact with the upper core layer and a gap layer lying between the upper magnetic pole layer and the lower core layer. The upper magnetic pole layer or the lower magnetic pole layer is formed of the soft magnetic film described.
Preferably, the area, adjacent to the magnetic gap, of the lower core layer or the upper core layer has at least two magnetic sub layers. Alternatively, the lower magnetic pole layer or the upper magnetic pole layer has at least two magnetic sub layers. The magnetic sub layer in contact with the magnetic gap is formed of the soft magnetic film.
Preferably, the magnetic sub layer which is not in contact with the magnetic gap is formed of a CoFe alloy having an Fe content X lower than that of the magnetic sub layer in contact with the magnetic gap.
Thus, the CoFe alloy for the soft magnetic film has a saturation magnetic flux density Bs of 2.0 T or more and a lower roughness. By using the soft magnetic film as a core material for thin-film magnetic heads, the magnetic flux can be concentrated on the vicinity of the magnetic gap to facilitate a high recording density. Also, corrosive resistant thin-film magnetic heads can be efficiently manufactured.
According to a methodical aspect of the present invention, a method of manufacturing a soft magnetic film comprising a step of forming a Co1-xFex alloy by electroplating with a pulsed current is provided. The Co1-xFex alloy has an Fe content X in the range of 68 to 80 mass %. The Fe/Co ion concentration ratio of the plating bath is in the range of 1.5 to 2.5.
In electroplating using a pulsed current, the current is intermittently applied by, for example, repeating on-off control by a current controlling device. By setting a pause time for applying no current, the CoFe alloy film can be gradually deposited, and the deviation of the current densities at plating can be alleviated in comparison with plating with a direct current. Thus, the electroplating with a pulsed current facilitates the control of the Fe content of the CoFe alloy to increase the Fe content of the film.
In addition, a Fe/Co ion concentration ratio of the plating bath in the range of 1.5 to 2.5 leads to a CoFe alloy having a Fe content in the range of 68 to 80 mass %, thus achieving a CoFe alloy having a high saturation magnetic flux density Bs of 2.0 T or more and a surface with a low center line average roughness Ra of 9 nm or less.
Preferably, the plating bath contains sodium saccharin to serve as a stress alleviator. Thus, the film stress of the CoFe alloy is lowered.
Preferably, the plating bath contains 2-butyne-1,4-diol to prevent the CoFe alloy from having a large crystalline grain size. Thus, the CoFe alloy has a small crystalline grain size and few voids among the crystals, hence having a smooth surface. As a result, the coercive force Hc is reduced.
Preferably, the plating bath contains sodium 2-ethylhexyl sulfate, which serves as a surfactant, to eliminate hydrogen generated in the plating bath, so that the formation of a rough film surface caused by the trapped hydrogen is inhibited.
Sodium lauryl sulfate may be used in stead of sodium 2-ethylhexyl sulfate; however, sodium 2-ethylhexyl sulfate foams less than sodium lauryl sulfate, and therefore a larger amount of sodium 2-ethyhexyl sulfate can be added to the plating bath to adequately eliminate the hydrogen.
According to another methodical aspect of the present invention, there is provided a method of manufacturing a thin-film magnetic head. The method comprises the steps of forming a lower core layer of a magnetic material, forming a magnetic gap, and forming an upper core layer. The upper core layer opposes the lower core layer with the magnetic gap therebetween at the face opposing a recording medium thereof. A step of forming a coil layer is comprised to apply a recording magnetic field to the lower and the upper core layers. The lower or the upper core layer is formed of the soft magnetic film by the method described above.
Preferably, the method further comprises a step of forming a lower magnetic pole layer of the soft magnetic film by plating on the lower core layer and at the face opposing a recording medium thereof.
According to anther methodical aspect of the present invention, there is provided a method of manufacturing a thin-film magnetic head comprising the steps of forming a lower core layer, forming an upper core layer, and forming a magnetic pole. The magnetic pole lies between the lower core layer and the upper core layer and has a shorter width in the track width direction than those of the lower and the upper core layers. The step of forming the magnetic pole comprises the sub steps of forming a lower magnetic pole layer on the lower core layer, forming a gap layer on the lower magnetic pole layer, and forming an upper magnetic pole layer between the gap layer and the upper core layer. Alternatively, the step of forming a gap layer on the lower core layer and forming an upper magnetic pole layer between the gap layer and the upper core layer. The upper magnetic pole layer or the lower magnetic pole layer is formed of the soft magnetic film by the method described above.
Preferably, the area, adjacent to the magnetic gap, of the lower core layer or the upper core layer is formed so as to have at least two magnetic sub layers. Alternatively, the lower magnetic pole layer or the upper magnetic pole layer may be formed so as to have at least two magnetic sub layers. The magnetic sub layer in contact with the magnetic gap is formed of the soft magnetic film by the method of manufacturing the soft magnetic film.
Preferably, the magnetic sub layer which is not in contact with the magnetic gap is formed of a CoFe alloy having an Fe content X lower than that of the magnetic sub layer in contact with the magnetic gap.
Accordingly, by forming the CoFe alloy for a soft magnetic film by plating with a pulsed current at an Fe/Co ion concentration ratio in the range of 1.5 to 2.5, the CoFe alloy can have an Fe content in the range of 68 to 80 mass %.
Using the soft magnetic film as a core material for thin-film magnetic heads results in an increased saturation magnetic flux density Bs, thereby achieving a high recording density. Also, corrosive resistant thin-film magnetic heads can be efficiently manufactured.